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Lesson 9, Topic 2
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# Excitation & Ionization Energies

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The energy absorbed or acquired by an electron to move to higher energy level is called excitation energy. Ionization energy is the energy absorbed by an electron to move it out completely from an atom.

An electron at ground state requires -13.6ev to free it from attraction of the nucleus.

Ionization energy of electron at first energy level is -3.39ev

Colour and Light Frequency

When an electron falls from a higher energy level to a lower energy level, it gives out excess energy in form of radiation. Therefore,

Frequency of radiation, f = $$\frac{\Delta E}{h}$$

Wavelength of height radiated in relation to quantum energy is

∆E = Ei – Ef = hf (where i and f indicate initial and final energy levels)

Ei – Ef = $$\frac{hc}{\lambda}$$

Wavelength and frequency are related to colours. Red light has a larger wavelength and low frequency while a violet colour has a shorter wavelength and higher frequency.

Example

The ground state energy for a hydrogen atom is 6.4×10-19J. If an electron drops from 22.8×10-19J energy to the ground state, calculate the frequency of the emitted radiation (h = 6.6×10-34Js)

Solution

E1 – E0 = hf

f = $$\frac{E_1 \; – \; E_0}{h}$$

f = $$\frac{2.28 \times 10^{-19} \; – \; 6.4 \times 10^{-19}}{6.6\times 10^{-34}}$$

f = -9.6×10-14Hz

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